Flexible metal conduits containing electrical wiring and end connectors sealed around the ends of the conduits are provided between electrical devices and junction boxes in environments where the electrical code requires sealed connections to prevent electrical sparks from gaining access to flammable materials through spaces left by an improper fitting or connection between the end connectors and the ends of the metal conduits which they envelope. The end connectors commonly are adapted to extend through openings in the housings of the electrical devices and junction boxes and receive nuts and sealing gaskets or the like which sealingly anchor the same to the housings.
One of the most important applications for such a flexible metal conduit with sealed end connectors is for lighting fixtures mounted in drop-ceilings forming a plenum in forced air heating systems. In such environments, code requirements are particularly severe with regard to isolating the electrical system from the air in the return plenum. In such case, while it would be desirable for the lighting fixture manufacturers to sell their fixtures with the attached metal conduit and sealed end connectors ready to be connected to junction boxes, because of the difficulty heretofore encountered in providing properly sealed pre-assembled end connectors for the conduits, the electrical contractors generally are given the responsibility of assembling the conduit and end connectors at the situs of the fixture installation. These end connectors, which usually included sealing rings and threaded connectors, are relatively expensive to install, and require special test procedures to determine if they provide effective seals. Moreover, it is desirable to prevent shock or arcing hazards which can be caused by inadequate or intermittent grounding of the conduit through the connectors due, for example, to vibrations applied to loosely mounted connectors. Also, using the connector constructions of the prior art it is often difficult to determine when the connectors are in the most ideal position on the conduit.
The conduit and connector assembly disclosed in my copending application Ser. No. 339,633, filed Mar. 18, 1974 and now U.S. Pat. No. 3,895,177, and that of the present invention comprise only a few parts, are easy to assemble into their ideal interfitting conditions, and they can be inexpensively and reliably fabricated in a factory so they require no testing or special assembly procedures at the situs of the fixture installation to ensure the proper sealing thereof. Thus, they can be mounted on the lighting fixtures by the fixture manufacturers in their manufacturing plants, so only their connection to junction boxes is required at the fixture installation.
In the conduit and connector assembly disclosed in said application Ser. No. 339,633, the conduit is a flexible open-ended spiral grooved metal conduit coated with a synthetic rubber-like plastic material which is air impervious, compressible and resilient. A connector assembly is provided at each end of the metal conduit which includes a coupling member with an air impervious metal sleeve portion enveloping the compressible resilient material at the adjacent end of the conduit, the metal sleeve portion having at least one and preferably three inwardly projecting continuous annular ribs pressed into the compressible resilient material without penetrating the same, to form at least one and preferably three continuous airtight seals between the sleeve portion of each connector and the compressible resilient material. Each coupling member has an outer flanged head portion which forms a wiring passageway communicating with the conduit interior and which is adapted to be anchored and sealed to the margins of a wall opening in the housing of an electrical device or junction box. Electrical connection between each coupling member and the conduit, which is generally required so the conduit may be suitably grounded, is provided by a resilient contact-forming member having a hollow longitudinally split shank and flank portions friction fitted within the adjacent open end of the conduit as by compressing the same slightly in the process of inserting the same into the conduit. The flange portion is in contacting relation between an axially inwardly facing shoulder formed on the head portion of the connector involved and the outer edge of the conduit, so it has a definite pre-determined position in the assembly.
The aforementioned annular ribs extending from the sleeve portion of the coupling member described above, as a practical matter, must be formed by crimping the sleeve portion of the member by a suitable rotating punch and die apparatus as disclosed in the aforesaid application. The sleeve portion must in this case be made of a material like aluminum which needs no protective coating. Thus, a connector made of a galvanized metal could not be used in this invention because the crimping operation grounds off the protective coating. Also, the grooving is aesthetically unpleasing and there is a small risk that the annular ribs formed by the crimping operation will severe the compressible resilient material or will not extend far enough into the compressible material to form a good seal.
The present invention provides a conduit and connector assembly having all of the advantages of the connector assembly disclosed and claimed in the aforesaid application without the use of an externally pinched or grooved sleeve which has the disadvantages referred to.
It is, accordingly, one of the objects of the present invention to provide a sealed conduit and connector assembly usable with a conduit of the type which has a spiral grooved construction and is coated with a seal-forming compressible resilient material, wherein the connectors which are sealed to the ends thereof comprise a few parts which may be simply, economically and permanently securely applied to the conduit at the factory and without the necessity for utilizing nuts, or externally grooved connector sleeves as in the case of the connectors disclosed in the aforesaid application.